Synchronous motors, including permanent magnet motors and line-start permanent magnet motors, are typically very efficient. However, synchronous motors such as these typically have limited capability to pull into synchronism loads that have a high torque or high inertia. Accordingly, the benefits in efficiency gains and energy savings ordinarily associated with synchronous motors are not typically achieved in applications having loads with high inertia and/or high torque characteristics. To achieve the benefits of efficiency provided by synchronous motors, for instance, line-start interior pole permanent magnet (LSIPM) motors, a coupling capable of concentrically contacting a shaft of a line-start synchronous motor may be used as an acceptable interface between the LSIPM motor and a high inertia and/or high torque load to improve long term operation of the system.